Stimulants such as methylphenidate are increasingly used for cognitive enhancement but precise mechanisms are unknown. We found that methylphenidate boosts willingness to expend cognitive effort by altering the benefit-to-cost ratio of cognitive work. Willingness to expend effort was greater for participants with higher striatal dopamine synthesis capacity, whereas methylphenidate and sulpiride, a selective D2 receptor antagonist, increased cognitive motivation more for participants with lower synthesis capacity. A sequential sampling model informed by momentary gaze revealed that decisions to expend effort are related to amplification of benefit-versus-cost information attended early in the decision process, whereas the effect of benefits is strengthened with higher synthesis capacity and by methylphenidate. These findings demonstrate that methylphenidate boosts the perceived benefits versus costs of cognitive effort by modulating striatal dopamine signaling.

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Psychostimulants such as methylphenidate are widely used for their cognitive enhancing effects, but there is large variability in the direction and extent of these effects. We tested the hypothesis that methylphenidate enhances or impairs reward/punishment-based reversal learning depending on baseline striatal dopamine levels and corticostriatal gating of reward/punishment-related representations in stimulus-specific sensory cortex. Young healthy adults (N = 100) were scanned with functional magnetic resonance imaging during a reward/punishment reversal learning task, after intake of methylphenidate or the selective D2/3-receptor antagonist sulpiride. Striatal dopamine synthesis capacity was indexed with [18F]DOPA positron emission tomography. Methylphenidate improved and sulpiride decreased overall accuracy and response speed. Both drugs boosted reward versus punishment learning signals to a greater degree in participants with higher dopamine synthesis capacity. By contrast, striatal and stimulus-specific sensory surprise signals were boosted in participants with lower dopamine synthesis. These results unravel the mechanisms by which methylphenidate gates both attention and reward learning.

Exerting cognitive control is well known to be accompanied by a subjective effort cost and people are generally biased to avoid it. However, the nature of cognitive control costs is currently unclear. Recent theorizing suggests that the cost of cognitive effort serves as a motivational signal to bias the system away from excessive focusing (i.e. cognitive stability) and towards more cognitive flexibility. We asked whether the effort cost of cognitive stability is higher than that of cognitive flexibility. Specifically, we tested this prediction in the domain of working memory by using (i) a delayed response paradigm that allows us to manipulate demands for stability (distractor resistance) and flexibility (flexible updating) of working memory representations, as well as (ii) a subsequent cognitive effort discounting paradigm that allows us to quantify the subjective effort costs assigned to performing the delayed response paradigm.We show strong evidence, in two different samples (28 and 62 participants respectively) that subjective cost increases as a function of demand. Moreover, we demonstrate that the subjective cost of performing a task requiring cognitive stability (distractor resistance) is higher than that requiring flexible updating, supporting the hypothesis that the subjective effort cost of cognitive stability is higher than that of flexibility.